The present invention relates to a resin composition, an electrically insulating prepreg, laminate and printed-wiring board using the resin composition, and methods for their production. The laminate referred to in the present invention includes a laminate one or both surfaces of which are clad with a metal foil, namely a metal-clad laminate.
In recent years, because of increasing concern about environmental problems, prepregs, laminates and printed-wiring boards for electrical insulation have been desired to release no harmful substances to the environment during their disposal or incinerate. Therefore, for the prevention of the so-called dioxin problem during their incinerate, the number of products characterized by containing no halogen-containing flame retarder is increasing. As a flame retarder that can substitute for the halogen-containing flame retarder, flame retarders of metal hydroxide type, phosphorus type, melamine-modified resin type and so on are employed and, especially, phosphorus-containing flame retarders are useful because a great flame retarding effect can be obtained by their use even in a small amount.
However, compounds practically used as a phosphorus-containing flame retarder include red phosphorus, phosphoric acid salts, phosphoric esters and so on. They have problems such as releasing harmful phosphine gas during their incinerate or reducing heat resistance or chemical resistance of laminates, printed-wiring boards and the like through their hydrolysis. With respect to such problems, JP-A Nos. 4-11662 and 2000-80251 disclose a reaction product resulting from an epoxy resin and an organophosphorus compound having a structure different from phosphoric esters and containing in its molecule a phenolic hydroxyl group capable of reacting easily with an epoxy resin. It is reported that this reaction product does not reduce heat resistance or chemical resistance and that flame-retardant resin compositions, laminates and printed-wiring boards containing no halogen-containing flame retarders can be produced using that reaction product. However, with respect to the reaction product resulting from an epoxy resin and an organophosphorus compound having a phenolic hydroxyl group disclosed in those patent publications, both of the epoxy resin and the organophosphorus compound are polyfunctional and, therefore, crosslinking structure easily occurs in the reaction product, it is very difficult to control their reactivity. Further, since an epoxy group is consumed when the epoxy resin and the organophosphorus compound react together, there are problems, with the reaction product, of having a very large epoxy equivalent and having a reduced curability.
Under these circumstances, an object of the present invention is to provide a resin composition that has enough flame retardancy without containing any halogen-containing flame retarder, has good heat resistance and good chemical resistance, and causes no problems with respect to reaction stability or curability caused by consumption of an epoxy resin through a reaction occurring during compounding of the resin composition. Another object of the present invention is to provide a prepreg, laminate and printed-wiring board using this resin composition and to provide methods for their production.
The inventors of the present invention investigated earnestly to attain the above objects and have found the invention below. That is, the present invention is directed to a resin composition comprising:
an epoxy resin,
an amine-type curing agent,
an organophosphorus compound having a structure represented by formula 1: 
Wherein R1 is an aryl radical with two hydroxyl groups, and the aryl radical can be substituted by one to three lower alkyls, preferably R1 is one of the radical selected from the group: 
and
an organic solvent,
wherein the epoxy resin and the organophosphorus compound have been compounded at a temperature of 50xc2x0 C. or lower. Further, the present invention is also directed to a prepreg, laminate and printed-wiring board using this resin composition, and to methods for their production.
The resin composition of the present invention is characterized by being a composition in which a reaction between the epoxy resin and the organophosphorus compound represented by formula 1 is inhibited until the resin composition is used for preparation of prepregs. If a reaction between the epoxy resin and the organophosphorus compound represented by formula 1 occurs during their compounding, the epoxy equivalent weight will change, resulting in a large variation in gelation time of the resin and an unstable curability. To control the reactivity of the two ingredients during their compounding, it is necessary to keep the temperature at 50xc2x0 C. or lower during the compounding step. Whether a reaction is taking place between the epoxy resin and the organophosphorus compound can be confirmed using a general-purpose analyzer such as high-performance liquid chromatography.
Examples of the epoxy resin contained in the resin composition of the present invention include bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, biphenyl-type epoxy resin, naphthalenediol-type epoxy resin, phenol-novolak-type epoxy resin, cresol-novolak-type epoxy resin, alicyclic epoxy resin, glycidyl ester resin, glycidyl amine resin, heterocyclic epoxy resin such as triglycidylisocyanurate and diglycidylhydantoin, and modified epoxy resins resulting from modification of these epoxy resins with various reactive monomers. Tetrakis(glycidyloxyphenyl)ethane can also be employed.
These epoxy resins can be used alone or, alternatively, two or more kinds of epoxy resins can be employed in suitable combination. Especially, phenol-novolak-type epoxy resin, cresol-novolak-type epoxy resin and dicyclopentadiene-modified novolak epoxy resin are preferable because high heat resistance and high reliability are required for electric and electronic material applications. It is desirable to use at least one of the three types of epoxy resins in an amount of 30 wt % or more versus the combined amount of the whole epoxy resin.
Examples of the amine-type curing agent that can be used include open-chain aliphatic amine such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexamethylenediamine, diethylaminopropylamine, dicyandiamide, tetramethylguanidine and triethanolamine; alicyclic amine such as isophoronediamine, diaminodicyclohexylmethane, bis(aminomethyl)cyclohexane, bis(4-amino-3-methyldicyclohexyl)methane, N-aminoethylpiperazine and 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5.5]undecane; and aromatic amine such as xylenediamine, phenylenediamine, diaminodiphenylmethane and diaminodiphenylsulfone.
These amine-type curing agents can be used alone or, alternatively, two or more kinds of amine-type curing agents can be employed in suitable combination. Especially, dicyandiamide is preferable from the viewpoints of curability and physical properties of cured products.
Examples of the organophosphorus compound having a structure represented by formula 1 include 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydroxy-6-methylphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydroxy-3-methylphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydroxy-4-methylphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 10-(1,4-dihydroxy-2-naphthyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. Especially, 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is preferable from the viewpoint of flame retardancy.
The compounding ratio of the epoxy resin, the amine-type curing agent, the organophosphorus compound having the structure represented by formula 1 and the organic solvent can be determined from the viewpoint of proper maintenance of the properties of cured products resulting from curing these ingredients, especially, heat resistance, hygroscopicity and flame retardancy. The amount of the amine-type curing agent compounded is from 0.3 to 0.6 equivalent per epoxy groups of the epoxy resin. The organophosphorus compound having the structure represented by formula 1 is preferably compounded in an amount of from 5 to 30 wt % in the organic solids excluding the organic solvent and the inorganic components.
The equivalent of the amine-type curing agent is defined by the molar number of active hydrogen bonding to the nitrogen atom present per mol of the curing agent. For example, when an amine-type curing agent is dicyandiamide, 1 mol is considered to be 4 equivalents. Compounding of the amine-type curing agent in an amount within the aforementioned range permits cured products to have enough crosslinking density and also to have controlled hygroscopicity. It, therefore, can result in the avoidance of problems concerning blister of a metal foil having thereon a circuit formed in a printed-wiring board manufacturing process, interlayer delamination and so on.
If the organophosphorus compound having the structure represented by formula 1 is compounded in an amount within the above-mentioned range, good flame retardancy can be exhibited. Further, since unreacted products do not remain in cured products during a molding and curing process, chemical resistance can be maintained.
With respect to the kind and amount of the organic solvent, any solvent can be used without any particular limitations if the epoxy resin and the amine-type curing agent constituting the resin composition can be homogeneously dissolved therein and the solvent has a viscosity and volatility proper for the preparation of prepregs. Particularly, methyl ethyl ketone, 2-methoxyethanol, 2-methoxypropanol, 1-methoxy-2-propanol and the like, which satisfy the above requirements, are preferable from the viewpoints of price, handlability and safety. The organic solvent is preferably used in an amount of from 10 to 50 wt % versus the total amount of the resin composition including the organic solvent.
Further, in the resin composition of the present invention, the epoxy resin and the amine-type curing agent may forgo phase separation to precipitate and the amine-type curing agent after the volatilization of the organic solvent during the production of prepregs depending on the kinds of the epoxy resin and the amine-type curing agent. In such a case, it is very probable that no uniformly cured products can be obtained when the resin composition as received is molded and cured. Therefore, a resin composition which can yield a uniformly cured product can be obtained by allowing an epoxy resin and an amine-type curing agent to react in an organic solvent at a temperature of from 80 to 140xc2x0 C. before compounding a composition, thereby bringing the two components into a state where the two components are mutually compatible in the absence of a solvent. It seems that the reason for this is that a bond is partially formed between an epoxy group of the epoxy resin and an amino group of the amine-type curing agent and the bond serves as a compatibilizer for these components. From the viewpoint of productivity, it is preferable for productivity that the reaction temperature is within that range because a sufficient reaction rate can be achieved and one can control the reaction. Further, in this step, a reaction accelerator can optionally be added. If an organophosphorus compound having the structure represented by formula 1 is added to such a mixture, the organophosphorus compound is added at a temperature of 50xc2x0 C. or lower after the reaction between the epoxy resin and the amine-type curing agent has been carried out.
The resin composition of the present invention can be prepared by holding the compounding temperature at 50xc2x0 C. or lower in the step of compounding the organophosphorus compound represented by formula 1. The reaction between the epoxy resin and the organophosphorus compound of formula 1 proceeds when a reaction catalyst is added and the system is heated to 100xc2x0 C. or higher as described in JP-A No. 1992-11662. However, even if the temperature is lower than 100xc2x0 C., the reaction proceeds slowly. If the temperature at which the two components are compounded is held at 50xc2x0 C. or lower, the reaction between the two components can be almost completely prohibited. Whether the reaction between the two components has proceeded or not can be confirmed using a general-purpose analyzer such as high-performance liquid chromatography. In the production method provided in the present invention, the reaction ratio, that is, the ratio of the amount of the organophosphorus compound that has reacted to the amount of the organophosphorus compound added is 0.5% or less.
To improve the flame retardancy, to enhance the rigidity or to reduce thermal expansion, the resin composition of the present invention can contain an inorganic filler. From necessity of achieving these purposes and limitation of maintaining adhesion and processability of laminates or printed-wiring boards to be produced from the resin composition, the content of the inorganic filler is preferably from 10 to 50 wt % versus the total amount of solid components excluding the organic solvent, that is, the resin solid components including the inorganic filler. The inorganic filler is not particularly limited and may be any non-halogen compound that does not deteriorate any property of laminates or printed-wiring boards, such as silica, talc, mica, aluminum oxide, magnesium carbonate and barium carbonate. Inorganic filler can be used alone or, alternatively, two or more kinds of inorganic fillers can be used in combination. Especially, aluminum hydroxide, which serves to improve flame retardancy, is preferable. It is most preferable to add aluminum hydroxide in an amount of from 10 to 50 wt %. To further improve the flame retardancy, it is effective to cover part of the inorganic fillers to be added with a molybdenum or zinc compound, and preferably with zinc molybdate, which combines advantages of both compounds.
The resin composition of the present invention may contain a flame retarder, a pigment, an adhesive aid, an antioxidant, and a curing accelerator and so on besides the above-mentioned ingredients. As such additives, known compounds can be employed. For example, various kinds of imidazoles (e.g., 2-ethyl-4-methylimidazole) can be used as the curing accelerator. Any non-halogen compound that does not deteriorate properties of laminates or printed-wiring boards can be employed in any content without any particular limitations.
A prepreg can be prepared by impregnating a substrate such as glass cloth with the resin composition of the present invention and drying. Further, a laminate can be manufactured by arranging a metal foil on the prepreg, and heating and pressurizing them to laminate together. Furthermore, it is also possible to manufacture a printed-wiring board by removing an unnecessary part of the laminate by etching. In the manufacture of the prepreg, laminate and printed-wiring board, the processes of coating, laminating and circuit processing usually employed in the art can be applied. The employment of these processes enables laminates and printed-wiring boards to possess high heat resistance, high flame retardancy and high reliability and containing no halogen-containing flame retarders.